The present invention relates to the use of electromagnetic waves for monitoring the volume of content within an enclosed media. More particularly, the invention relates to an electromagnetic wave analyzing method and system for monitoring the volume of urine in the bladder.
The urinary system is composed of two kidneys, two tubes called ureters, one urinary bladder, and the urethra. The kidneys are bean-shaped organs that produce urine. They are protected by fibrous connective as well as adipose tissue. The kidneys maintain homeostasis by regulating the water and salt balance as well as the pH of the blood, and they excrete nitrogenous wastes generated by amino acid, uric acid, and creatinine metabolism. The ureters are muscular tubes that lead away from a kidney and convey urine to the urinary bladder, which is a distensible, muscular organ that stores urine until it can be expelled. When the urinary bladder fills with urine to 250 of its total 600 milliliters and more, stretch receptors send impulses to the spinal cord. Urination results when returning nerve impulses cause the sphincters to relax and the bladder to contract, so, normal function of the lower urinary tract, including the bladder and the urethral control (sphincteric) mechanism depends on an intact spinal cord.
Urinary incontinence is the inability to control urination. The term may be used interchangeably with Over Active Bladder (OAB) which also includes the same frequency in urination and urinary urge. It is estimated that over 12 million Americans have urinary incontinence. Incontinence affects all ages, both sexes, and people of every social and economic level. It is also estimated that 15 to 30 percent of people over the age of 60 who live at home have incontinence. Women are twice as likely as men to have this condition. Bladder dysfunction can be caused by spinal cord injury, brain injury or diseases that impair the nerves to the motor neuron or upper motor neuron. Neurogenic bladder is a general diagnosis commonly used and refers to altered bladder function resulting from interrupted nerve innervation due to a lesion of the central or peripheral nervous system. Damage to nerve pathways at any point between the cortical center in the brain and the bladder can impair normal bladder function leading to incomplete bladder emptying. The type of bladder dysfunction seen depends on the exact site and the extent of the lesion. Diffuse neurologic damage, such as that from multiple sclerosis, Parkinson's disease or spinal cord injury can produce the inability to initiate or adequately complete voiding.
Post-void residual (PVR) urine volume is the volume remaining in the bladder immediately after completion of voiding (emptying). Knowing the PVR is important in patients suspected of incomplete bladder emptying or urinary retention. Usually, a person may maintain some ability to void, but elevated PVR lead to an increased risk of acute urinary retention, urinary tract infection, or upper tract pathology such as pyelonephritis, hydronephrosis or renal insufficiency. Urinary retention is determined by measuring the post-void residual (PVR) urine volume. A PVR volume of greater than 100 mL is generally accepted as the criteria to define urinary retention. In elderly patients, however, a PVR of 150 to 200 mL or greater indicates incomplete bladder emptying. Urine remaining in the bladder after the person has voided can become colonized with bacteria. The measurement of PVR urine volume is also an important component of continence assessment and bladder management during bladder retraining programs for patients with spinal cord and brain disorders which cause bladder dysfunction. Measurement of PVR urine volume provides quantitative feedback to the patient and the rehabilitation team about the effectiveness of the voiding technique.
The standard method of determining PVR urine volumes is intermittent catheterization, which is associated with increased risk of urinary infection, urethral trauma and discomfort for the patient. Bladder ultrasound scanning has been introduced as an alternative, noninvasive method, to avoid the potential complications of intermittent catheterization. Using this method, PVR urine volume can be measured immediately after a patient voids (if necessary, between scheduled catheterizations), which increases feedback about voiding technique used during bladder retraining. Early studies of ultrasound in this application were done using large scanners, which were relatively immobile. These ultrasound methods required separate calculation of the total bladder volume and of the PVR urine volume.
During the last decade there have been significant developments in bladder ultrasonography. Portable, battery-powered ultrasound devices have been developed specifically for the noninvasive measurement of total bladder volumes and/or PVR urine volumes. They consist of a hand-held ultrasound transducer (scanhead) and a base unit with a display screen. The scanhead is placed on the patients' abdomen (suprapubic area) and aimed toward the bladder. The unit calculates and displays the bladder volume.
Extreme obesity, severe abdominal scarring, pregnancy, muscle spasms, abdominal herniation and abdominal breathing may interfere with bladder ultrasound scanning and prevent accurate measurement.
The main question concerning the use of an ultrasound device to assess the PVR urine volume during bladder retraining is whether this method can accurately identify patients with more than 100 mL of urine in their bladders.
Several studies have been conducted to determine whether bladder ultrasound scanning for the measurement of PVR urine volume during bladder retraining in stroke patients and spinal cord injured patients is as accurate as the measurement obtained by catheterization. Results of these studies suggest that ultrasound measurements of PVR urine volume have some limitations in regard to accuracy. There is some opinion that more accurate results are obtainable through separate calculation than those that are automatically calculated by available ultrasound devices. Institutions using this technique should have appropriate training and operating protocols in place and be aware of its accuracy under local practice condition. The main problem in using such methods is the sensitivity to changes in the direction of the transducer. Ultrasonic systems are not automatic and require the intervention of a skilled user. Numerous attempts for monitoring the volume of urine in the bladder have been made in recent years. U.S. Pat. No. 6,319,208 discloses a urine monitor system, the system comprising a pressure measurement device capable of using magnetic induction telemetry. The invention may be used in measuring urinary tract pressure in diagnosing and treating urinary tract infections, anomalous bladder contraction, etc.
U.S. Pat. No. 5,964,710 proposes a system for estimating the volume of fluid in the bladder by sequentially scanning the bladder with ultrasonic beams that section the bladder into a number of transverse planes. After determining the area in each of the planes, the system determines the volume of the bladder by summing weighted version of the planar areas.
In addition, U.S. Pat. No. 6,110,111 includes means for automatically scanning the bladder of the user with ultrasound signals. The returning signals are used to calculate the volume of urine in the bladder and also to calculate the actual surface area of the bladder.
U.S. Pat. No. 5,103,835 proposes a monitoring device for preventing urinary incontinence which is based upon detection of electrical impedance. A monitoring device for preventing urinary incontinence has the following components: a high-frequency constant-current power supply adapted to supply a pair of terminals which are set on the surface of a human body across the urinary bladder; a high-frequency voltage signal detecting means which conducts wave detection from a high-frequency voltage signal sensed by a pair of sensing electrodes which are set on the human body surface at positions on the path of the high-frequency electrical current flowing between the pair of terminals;
In addition, U.S. Pat. No. 5,235,985 discloses an automatic bladder scanning apparatus. This apparatus is included in order to produce information concerning the three dimension image of the bladder, said information then used to calculate the bladder volume.
None of the existing methods and apparatuses described above proposes an apparatus which is non-invasive, automatically monitoring the bladder measurements, simple to use and cost effective.
The present invention evaluates bladder function without the use of invasive instrumentation, such as catheterization, using a multi-frequency electromagnetic wave analyzing method and apparatus for monitoring the volume of urine in the bladder.